Solar savings & assumptions
Start with the assumptions.
Any financial figure for solar is the result of a chain of assumptions — about generation, household use, self-consumption, tariffs, export and future prices. Understand the chain and the figure becomes easier to judge.
Outcome · Depends on
- Generation
- Estimated
- Use
- Household-specific
- Tariffs
- Can change
- Figures
- Proposal-specific
Savings depend on more than system size.
- 01
SOLAR GENERATION
An estimate, shaped by roof, equipment and weather.
- 02
HOME USE
When and how much electricity the household uses.
- 03
SELF-CONSUMPTION
The share of generation used in the home as it is produced.
- 04
GRID IMPORT / EXPORT
What is still bought in, and what may leave the home where arranged.
- 05
ENERGY TARIFF
Import rates and any export rate — both can change.
- 06
FINANCIAL OUTCOME
The result of all of the above, under stated assumptions.
* Export only where suitable metering and an export arrangement exist.
Six assumptions behind every figure.
| Assumption | What it is | Where it comes from | How it can change |
|---|---|---|---|
| 01 Generation estimate | How much the system is expected to produce in a year. | Roof, equipment, location and loss assumptions. | Varies with weather and performance. |
| 02 Household use | How much electricity the home uses, and when. | Bills, supplier account data or the homeowner. | Changes with routines and appliances. |
| 03 Self-consumption | The share of generation used in the home as it is produced. | The overlap between generation and household use. | Depends on who is home, and when. |
| 04 Electricity tariff | The price paid for imported electricity. | The household’s current supplier and tariff. | Tariffs can change. |
| 05 Export | Any payment for surplus electricity sent to the grid. | Metering and any export arrangement with a supplier. | Terms and eligibility can change. |
| 06 Future prices | What electricity might cost in years to come. | Unknown. Any assumption should be stated. | Uncertain — can rise or fall. |
Same roof, two households.
Household A · Usually occupied
More daytime use overlaps with generation, so more solar electricity can be used as it is produced.
Household B · Usually empty
Most use falls in the morning and evening, so more generation may flow to the grid during the day.
Solar generation (shape only) Household use (shape only). Illustrative, not to scale.
Nobody knows future energy prices.
Questions
Savings questions
How much will solar panels save me?
That cannot be answered without a project-specific proposal. Potential financial outcomes depend on the property, system, electricity use, tariffs, export arrangements and other assumptions.
Why don’t you publish typical savings or payback periods?
Because a typical figure would describe nobody’s home in particular. Generic savings percentages and payback periods can be misleading. Any financial figure belongs in a project-specific proposal alongside the assumptions behind it.
Does being at home during the day make a difference?
It can. Solar electricity used at the moment it is generated replaces electricity that would otherwise be imported. Households that use more during daylight hours can often use more of their own generation.
What should I check in a proposal’s savings figures?
Look for the generation estimate and its method, the electricity use assumed, the self-consumption assumed, the tariff and export rates used, any assumption about future prices, and whether figures are described as estimates.
Proposal · Conversation
What could solar look like on your home?
Tell us about the property and household electricity use to begin the conversation.
No obligation. Nothing is sold through this website.